Work vehicles, such as fork lift trucks, experience longitudinal instability when overloaded or improperly loaded. A lift truck, for example, experiences longitudinal instability when attempting to lift a load which is too heavy and when traveling over a rough or uneven pathway. When overloaded, the lift truck tends to pivot about the front axle and the rear-mounted steering axle sometimes leaves the roadway.
An increase in load placed upon the front mounted forks results in a decrease in deflection of the rear mounted steer axle. Thus steer axle deflection is useful as an indication of the load condition of the lift truck. A deflection sensing device is used to monitor steer axle deflection and indicate the load condition of the lift truck.
A stop member is mounted on each side of the lift truck between the body or frame and the steer axle. The frame and axle contact one of the stops when the lift truck operates on a sufficiently rough pathway and limits pivotal motion of the axle toward the vehicle frame. Axle deflection is decreased when the stop is contacted giving the false impression that the lift truck is overloaded.
It is desirable to sense impending longitudinal instability to prevent damage to the lift truck or materials being handled. This sensing is desirable to prevent operation with a greater load when a stop is contacted than when not and is realized only when the sensing device is positioned at the location where the deflection moment of the axle is not affected by the stop member contacting the axle.